The episode which aired on Thursday, April 20, 2017, saw the shocking death of Elizabeth North, Mellie's chief of staff.
The character which was killed by the season's villain, Zoe Perry, was beat to death with a golf club.
It was my decision but not because I no longer wanted to be part of the show, Portia said to Hollywood Reporter.
It was more because I found a great business opportunity I wanted to pursue that was taking my interest away from acting and a career I've had for 20-plus years and putting it elsewhere that was very timing consuming.
"I approached Shonda and asked if it would be OK if I could leave Scandal. She was nothing but supportive and wished me luck in my business venture and was gracious and lovely about it."
Following her death, Ellen DeGeneres took to Twitter to praise her wife ’s performance on the show.
Scandal creator Shonda Rhimes saluted de Rossi for her contribution to the political drama, which features Kerry Washington as top fixer Olivia Pope.
"I have been a fan of Portia's for years and it was an honor to have her join our Scandal family. Portia infused Liz North with a smart, powerful, vulnerable soul while also making the humor sing, and that brought all of us in the writers room a lot of joy," Rhimes said.
"If I could keep her forever, I would , but kidnapping is illegal. Besides, I am incredibly impressed with the vision she has for her creative future. I wish her all the best.”
Portia's exit is the second time in the show's six-season run that a regular cast has been killed off. The first was Harrison, played by Columbus Short, who was killed off on-screen following domestic violence allegations off-screen.
Portia de Rossi joined the Shonda Rhimes' created show in season four.